Will a comet clobber Mars next year?

On January 3, 2013 comet C/2013 A1 was discovered photographically by Robert McNaught at Siding Spring Observatory in Australia. At the time it was over 7 times farther than Earth from the sun and extremely faint. Though far from Earth’s perspective, this dusty dollop of ice had probably been on its way from the Oort Cloud, a massive and distant comet repository at the fringe of the solar system, for millions of years.

Comet C/2013 A1’s orbit cuts a steep path through the plane of the planets. Right now the comet is well below the plane but is on its way “up”. On October 19, 2014, it will pass extremely close ot Mars. Credit: NASA/JPL

Although not expected to pass particularly close to Earth next year, the comet will have a very close brush with Mars. Leonid Elenin, Russian comet hunter and discoverer of the famed Comet C/2010 X1 Elenin, has examined C/2013 A1’s orbit and found there’s a small chance it could collide with the planet Mars on October 19 next year.

Based on 74 days of observations plus the latest data from Elenin, which admittedly only cover a short piece of the comet’s arc, A1 could zoom as close as 22,990 miles (37,000 km) from the surface of Mars and shine 40 times brighter than Venus at magnitude -8.5 … as seen from Mars that is. Earth observers will see it around 8th magnitude, so you’ll need a pair of binoculars at minimum.

Since a comet’s tenuous outer atmosphere – called a coma – is typically around 62,000 miles (100,000 km) across, C’/2013 A1 is practically guaranteed to give the planet a gentle powdering.

Diagram showing how the orbit of the comet intersects the orbit of Mars on October 19, 2014. Credit: Leonid Elenin

Given the close brush, there’s even a possibility – for now – that it might crash right into the Red Planet.

This is where things get interesting. Astronomers estimate a comet’s size by measuring how its brightness changes during its approach to the sun. C/2013 A1 turns out to be a potentially BIG comet with a diameter estimated at up to 31 miles (50 km) across.

Its orbit is also tipped over so far (greater than 90 degrees to the plane of the solar system) A1 travels in retrograde motion opposite the direction in which the planets move around the sun. Should it aim for Mars, the two bodies will hit head-on with the comet speeding at 35 miles per second. Dare I say, the energy released from the impact would be prodigious.

Here’s Elenin’s take: “This kind of event can leave a crater 500 km (310 miles) across and 2 km (1.2 miles) deep. Such an event would overshadow even the famous bombardment of Jupiter by the disintegrated comet Shoemaker–Levy 9 in July 1994, which by some estimates was originally15 km (9 miles) in diameter.”

A blast that powerful would easily be visible from Earth as a brilliant flash of light followed by a massive cloud of debris expanding over the Martian landscape and high into the planet’s atmosphere. From Mars, the event could be photographed by one of several Mars-orbiting satellites or even the Curiosity rover. Even if the comet misses the planet, we’d hope NASA or ESA (European Space Agency) could point a camera to take the first-ever photos of a comet from another planet.

The view from mid-northern latitudes facing southwest on October 19, 2014 when the comet and Mars will be extremely close in the evening sky after dusk in Ophiuchus near the “Teapot” of Sagittarius. The path shows the comet’s position every five nights. Created with Chris Marriott’s SkyMap software

Could this all be crazy talk? Maybe. In order to make a firm prediction of exactly what path the comet is on, astronomers will accurately measure its position and refine its orbit in the coming months. Chances are, it won’t hit, but the possibility remains … for the moment.

As for Earth, we’re in the the clear. C/2013 A1 will miss us by 84 million miles even when closest in early September next year. If we assume for a moment that the impact will happen, sky watchers in the eastern hemisphere will have the best seats. I checked the the positions of comet and planet in SkyMap, a highly accurate planetarium program, and determined the time of closest approach to be around 5:30 a.m. Central Time Oct. 19, Mars won’t be up in the sky for the U.S. but will be for much of Russia, China and other eastern hemisphere countries. For observers there, a possible impact would occur during early evening hours on Oct. 20.

Mars will be in the constellation Ophiuchus at that time and low in the southwestern sky at the end of evening twilight. For observers in the U.S., Canada and South America, the planet and comet, should it survive, will be only about half a degree apart at dusk the evening of the 19th. Big blast or not, they’ll certainly make for a memorable sight in a telescope.

23 Responses

Please forgive me but I just wanted to point out the typo in the caption under the 1st comet`s orbit diagram where the date of the Mars close approach is off by a year.
Thank You for the quality and quantity of information that appears on the blog.

Hi Kevin,
The original story I saw yesterday written by Leonid and translated by Maksim Kakitsev reads this way:”up to 50 km”. He then goes on to estimate the impact energy based upon that number. There was no mention of 10km – at least not there. Yes, the 74-day arc indicated a farther pass – something like 66,000 miles – but when I checked Elenin’s site this afternoon his new observations changed the closest approach to 22,990 miles. I wanted to be sure to let readers know that was the latest data – that’s why it’s noted in the article. Thanks for your comment.

I would estimate that it will take an observation arc of closer to 120 days to get a significant improvement over the 74 days observation arc (that as of Feb 27th only includes observations through Feb 20th.)

Comets, Mars and October, also the close pass of the red planet by ISON this October 1, when the comet could be nearing magnitude 8. Think of the impact, SL9 would have had with Jupiter if it had hit as one solid comet, instead of fragments.

Peter,
Phobos is 5,825 miles from the planet so it wouldn’t seem likely unless the comet hit solid and intact, and the moon was in the right position at the time of impact to intercept outbound debris.

Jan,
Great question. Yes, an approach that close would probably change it path to some degree, similar to how Earth re-shapes the orbits of very-close-approaching asteroids. And thank you for your kind words about the blog. Very happy to have you as a reader.

Just wondering: since this comet is a year and half away, and since it may be very large as comets go (10-50 km diameter would be very large for a comet, wouldn’t it?), would that make it a good ‘target’ to try to rendezvous a probe of some sort? Would such a thing be possible in that kind of time frame?

Hi Bob,
Good question. I doubt it otherwise we’d have heard by now. A year and a half seems too little time to build a craft, launch and rendezvous. Deep Impact, which has flown two successful missions to comets, is currently en route to asteroid encounter, so we can’t use that. Stardust has been switched off and other missions I’m aware of are targeted to other objects. Sure would be cool if some upstart space agency like SpaceX entered the game.

Such a large comet getting this close to a terrestrial planet must be *extremely* rare. Mars will likely be entirely engulfed by its coma on closest approach!
This list shows comets coming to within 1/10th an AU, about 15 million km, of Earth:

None came closer than .015 AU, about 2.2 million km, during a 400 year period. But this comet is supposed to get within almost 1/100th that distance to Mars!
Given the unusual close encounters the Earth has had recently, I think there should be an investigation into a physical cause for these close approaches, not just coincidence.

Hi Bob,
While a rare event for a comet, it’s not rare when you consider all the small bodies out there – in particular asteroids. Lots of asteroids come that close or closer to Earth (and probably Mars) every year. I don’t think there’s a particular physical cause especially given the rarity of comets doing this. Now if comets routinely passed this close to Mars, we might consider looking for a mechanism.